Samstag, 27. September 2008

"The reason why geologists are privileged, among scientists, to slip into such naivety has to do with their training as creators of stories based on rather slim evidence (a fact remarked on by Mark Twain). For example, we can look at some piece of rock in Kansas or northern Germany, and tell a wonderful story about enormous glaciers carrying that rock over hundreds of miles, thousands of years ago. My point is that those who reconstruct geological history are engaged in a type of myth making, an activity carrying the risk of being assigned to the lunatic fringe by the less adventurous, and yet an activity that is potential fruitful."

BERGER (2007): On the discovery of the ice age: science and myth. From Piccardi & Masse: Myth and Geology. Geological Society, London, Special Publications, 273: 271-278

A team of geophysicists at the University of Texas travelled to Tonga last November in search of rumoured reports of large out-of-place erratic boulders located along the western flank of Tongatapu. During their expedition, the researchers found a 3 km chain of massive coral boulders that had been deposit 100-400 m inland. The analysis suggests these boulders may represent the largest known tsunami deposits on Earth. Radiometric dating and structural/sedimentary interpretation indicates these boulders may have been emplaced recently (Holocene).

The boulders lacks a pronounced soil or vegetation cover, letting conclud that they are relatively "young".

A boulder thrown on land by the catastrophic tsunami as consequence of the eruption of the volcano on Krakatoa in 1883.

In some areas of Europe or North America, you can find also strange boulders, with diameters ranging from meters, weighing probably 100 of tons, lying on flat terrain, with no apparent source wall where the possibly felled off. They often even don’t resemble the same geology of the surrounding landscape and the underlying underground, for example you can find large boulders of carbonates on a crystalline basement.

Local legends often attributed the position end existence of this stones to the work of the devil. To get a human soul he had to build a wall or a building in just one night, but when he realized that he couldn’t finish the work, he just let fall the stone that he was carrying from the mountains down to the plain – and so you can find it lying there until today.

Other legends tell us, that they where playthings of giants, a notion that is reflected in common language to the present day, in southern Sweden the "giant" erratic rocks are “things thrown by giants”.And finally a legend from Tongatapu tells us, that the god Maui throws the rocks from the sea on the land, trying to kill a giant, men-eating chicken.

But the so called erratic boulders remained for much longer time then the local legends where told one of the most puzzling mysteries for geoscientists. In the 18 and 19th century one of the discussed scientific explanations was, that the observed boulders where deposited by a large flood or Tsunami (by some attributed directly to the biblical flood story).

The first descriptions of erratic boulders are attributed on some authors of the early 18th century, like Karl Nicolaus Lange (historian, living from 1670 to 1741) in the year 1708, or 1715 by Lars Roberg (doctor in medicine from Upsala, living from 1664 to 1742).Berner Gottlob Sigmund Gruner realized in 1774 that the source region of the boulders (denominated “Geißberger”) found on the plain forelands of the Alps, were in fact the mountains of the Alps. He also had studied intensively the glaciers in the Swiss mountains.But the most convincing hypothesis for the time on the genesis of the boulders was presented by the swiss naturalist Horace Benedict de Saussure (1740-1799). He had climbed mountains around Geneva since 1758, and after 1760 he travelled more than 14 times trough the Alps (considering the possibilities in this time an extraordinary achievement).He explained: the rocks were transported on their recent locations by an immense flood. That seemed to explain why most of the boulders found scattered around the plains of Germany came in first place from the regions of Scandinavia, where the same lithology where found in the crystalline continental basement, like Precambrian metamorphic rocks and paleozoic sediments. The theory worked lesser to explain the foreland rocks - to transport boulders from the Alps, the flood at least had to reach 1000 of meters.

Large floods are known to have occurred in the geological past trough the deposits and sediments that we found, but only local, and never capable to flood entire continents. The amount of (liquid) water needed to transport large boulders for hundred of kilometres were unrealistic.

Bristow, H.G. (1872): The world before the deluge by Louis Figuier - Newly edited and revised by H.W. Bristow. 2nd. edition - Cassel, Petter, Galpin & Co. Only after 1875 the explanation, that glaciers transported the erratic boulders, was accepted universally.

Around the first decades of the 19th century books like Agassiz “Etudes sur les glaciers.” (published 1840) showed that glaciers can easily transport debris and huge boulders (he wasn’t the first, but his authority helped him to propagate the idea).But the observation on the studied glaciers in the Alps leaded Agassiz to a even more heretic idea – glaciers not only are important geological factors in high altitude regions, but glaciers and ice covered large areas of Europe, North America and Asia in the geologically recent past, and transported debris for hundred of kilometres, where it was deposited after the glaciers melted and retracted to their modern extension.

Montag, 22. September 2008

The last years have seen a new kind of exploration, robots and space probes have given us insights in the (in part) icy geology of the “rest” of the solar system. But there are also fire worlds, strange tectonic settings, gas giants, where the laws of geology don’t rule no more, eternally frozen worlds… So it was only a matter of time, until the Accretionary Wedge has conquered the deep space, where no geologist is gone before… on goodSchist.com

Silver Fox takes a look on the possible future Gold-Iron-Nickel rush in the frontier asteroid rim. But asteroids, and their impacted counterparts’- meteoroids, are not only good to delivery elements trough space, but also create important geomorphic features on the planets of the solar system, like shown by ed.And speaking from amazing geomorphic features, ever seen a reversed fluvial topography on Mars?Space can be a very hot place, so hot that new elements can formed, but still so cold that all geology is based on ice or liquid gases, like on Titan 1 e 2.A often forgotten world of ice is Pluto, the declassified planet. On the other side there is the hell (tectonic) on Venus, or the molten small moon Io.

(This is just a selection of the submissions on the Accretionary Wedge - for the complete list visit the side of Chris I´m still ongoing reading ...)

Samstag, 20. September 2008

The computer models used in climate change prediction lacks an important factor – the change in permafrost geographically extension and depth. Covering at least 22 to 38 millions square kilometres, mostly in circumarctic belt, it is thawing.

But still data about the mostly hidden ground ice is not complete, about his change and the impact of this change on the climate, for example trough the release of methane in the atmosphere.

Canadian researchers have published now an article in “Science” (Nr. 321, pag.1648) about an important find – impossible (or at least improbable) permafrost.

Duane Froese and colleagues of the University of Alberta have discovered ice wedges near the Dominion Creek in the Yukon, dated at least having 750.000 +- 60.000 years –the oldest ice of the nordamerican continent.

The ice is conservated in a depth of 3 to 4m under the modern landscape level, and was dated with ash-layers incorporated in the ice (Gold Run Tephra). This age implies that the ice has “survived” warm periods in the past, like the Eem-interglacial (126.000-115.000), considered so warm or even much warmer then the Holocene.

The researches do not dispute the fact that modern permafrost is thawing. Maybe the Canadian discontinuous permafrost reacts slower then previously though on climatic change, or the soil provides enough isolation to buffer warmer temperatures for longer periods.

Old ground ice is also known from permafrost in Siberia, but younger, with “only” 200.000 years.

Now only more discoveries of this kind can provide a clue if this are only local exceptions, or global warming is not consistent on the entire planet, or that there is the possibility that permafrost reactions to a warmer climate are more complex then we think and simulate.

"No one would have believed in the last years of the 20th century that this world was being watched keenly and closely by intelligences other than martians's and yet as mortal as his own. Yet across the gulf of space, minds that are to our minds as ours are to those of the beasts that perish, intellects vast and cool and unsympathetic, regarded this mars with envious eyes, and slowly and surely drew their plans against us. "

From all planets and minor objects of the solar system, most similarities to features of periglacial regions on Earth can be found on the red neighbour - Mars.The term periglacial refers here to immediate results of frost as climatic factor acting on soil substrat/detritus (geologic component).

Even if the terminus is mostly debated and in part imprecise, he can be summarized as “conditions, processes and landforms associated with cold, nonglacial environment”.

Permafrost – perennially frozen soil- is one diagnostic criteria for a periglacial environment, that can, but mustn’t contain ground ice. In the last case it can be called “dry permafrost”, but it plays a minor role in the development of characteristics or spectacular landforms of the periglacial realm.The most spectacular forms of permafrost imply the presence of water and ice. Pingos (or hydrolaccolith), literally small mountains, contain a core of pure ice, and can reach up to 50m high. Other features that imply frozen water are ice-wedges or ice-lens and bodies.Important macroscale features of permafrost are rockglaciers. Rockglaciers can best be defined by their morphology, saying that a rockglacier is “an accumulation of angular rock debris that contains either interstitial ice or an ice core and shows evidence of movement through creep and deformation of the ice-part”.

The presence of ice on Mars was never questioned. Even the first modern geographical maps by american astronomer Richard Antony Proctor from 1867 located two huge icecaps on both the poles. Today we know that the polar ice caps of Mars contain at least a part of water-ice, but it seemed not so extraordinary much, in ever case lesser, then some author speculated needed for a civilisation on Mars.

The question still remaining –even today- is, how much ice, and so water exist on Mars, and where else it can be found, in an atmosphere with so less pressure that it is prohibiting that water can exist in liquid form (at least for a longer period)? Models showed that a cover of detritus could prevent the ice to sublimate, so allowing in theory in some regions great amounts of subsurface ice, and maybe even liquid water. But how to prove the existence of this modelled ice?

Landforms indicative of ground ice on Mars have known since the first flyby missions of the 1960s. Images from Viking orbiters provided an overwhelming list of permafrost and ground ice indicators.Mars resembles an astounding variety of landforms that on Earth can found in recent glacier covered, and/or in past glaciated areas, like patterned ground, thermokarst, mass movement phenomena, cirques and horns, grooves and valley troughs filled with morain-like material. On earth they are declared to prove glacial to periglacial conditions and glacier ice. On the other side, on Mars there exist a lot of forms that have no counterpart on Earth.

The most recent space probes measured the emission of neutrons from the surface of Mars. Water ice adsorbs more neutrons that dry detritus, so mapping the amount can be used to map and estimate the presumed water ice content of the first meters of the surface detritus, the so called regolith.

Fig.1. Watercontent in percent of weigth of the martian regolith, ranging from 3% (light blu) to 11% (dark blue). The presence of water ice is correlated with latitude, radiation and elevation/temperature. Red zones are areas with dense numbers of "debris aprons" (after KERR 2003).

The Phoenix Mission finally discovered subsurface ice covered only by centimeters of some dust and detritus on the high latitude (ca. 70°N) of the northern hemisphere. But still they prove only an ice content up to 6-11% in the first 1 to 2 meters of the regolith.

On Mars there are different types of features whose morphology certainly indicate the presence of deep buried ground ice - rampart craters, debris flows, lobate debris aprons, terrain softening and collapsing and patterned or polygonal terrain.

Many martian craters have a unique morphology - they are surrounded by lobes or tongues with layered ejecta, terminating in a low ridge or escarpment. This “rampart craters” are unique for Mars in our solar system, and probably represents refrozen ejecta from an impact that melted the subsurface ice-rocks mixture.

Most curious and debated are very large features, up to hundreds of kilometres long, that shows ridges and furrows on their surface, and seem to flow along rock walls and follow valleys.

- and lobate to tonguelike shorter mass movements, that initiate from a rock wall, shows a pronounced ridge and furrow morphology, and end with a gently slope on flat terrain.

Fig.2. Infrared MOC-image, east of the Hellas-basin, Mars. A typical association of debris aprons, debris tongues and crater fills. Note the superimposed features in the center of image. Scale in 100 kilometers.

Interpretations range from lavaflows, that some features resemble, to vast mass-movements and rockfalls deposits.The huge aureole deposits, that form a ring extending up to 1.000km around the basal escarpment of Olympus Mouns, were also interpreted to represent immense submarine landslides.

Studies on (primarily mentioned) terrestrial rockglaciers and debris-covered glaciers in recent years offered a new explanation – the rockglacier like features on Mars are - according to the duck test … rockglaciers.

Fig.3. Terrestrial rockglaciers, Alps. Scale in 100 of meters. Showing a tongue like rockglaciers, and two "lobate debris aprons".

A rockglacier can be active - containing enough ice to show creep and deformation, inactive – still containing ice, but to less to show movement, and relictic – containing no more ice, but still displaying the morphology of past movement

Under modern climatic conditions on Mars, and assuming a behaviour comparable with terrestrial rockglaciers in Antarctica, the rockglaciers on Mars can possibly be active containig both water as CO2-ice in a belt stretching approximately on the 30° latitude (Fig.4).

Fig.4. Martian rockglaciers. Mean elevation data map (blu - deep, red - high) showing areas with high density of lobate debris aprons, like east of the Hellas basin, the chaotic terrain from Deuteronilus and Protonilus Mensae, the west escarpment of Olympus Mons and the Argyre basin.

MOC (Mars Global Surveyor Camera) Orbiter images of lineated valley fills and lobate debris aprons show that the surface of this features are practically uncratered, indicating likely emplacement and formation within the past several million years. With this method, the lobes of Olympus Mons were dated to be polygenetic with ages ranging between 280-130, 60-20, and -surprisingly- 4 million years and younger.

Fig.5. The west escarpment of Olympus Mons, with pronounced lobes (note the ridges)expanding for more then 200 km (scale) - some authors interpreted the morphology as deposits from glaciers, or remanents of debris covered glaciers. It is unclear however if they still contain ice.

However at current Mars surface temperatures, and very low accumulation rates of material, flow rates large ice masses would be so slow, that they could not be younger then 1 to 10 millions of years, but still much older then the crater counting let conclude. But assuming higher past temperatures in geologically speaking recent times, a young age became more convincing.Overlapping tongues seen on some lobes even let assume that they were periodically active, implying possibly glacial and interglacial periods on Mars, driven by the steep tilted axis of Mars (15-35°).

The distribution of the presumed activ and relict rockglaciers seem to support this hypothesis, they only occur in a narrow belt of 30 to 50° of latitude on both hemisphere, region that in past “passed trough” the climatic zone that enables the formation of great amounts of ice and activity of rockglaciers (Fig.4.).

Discovery of microbial activity inside of active terrestrial rockglaciers give room for speculation that rockglaciers on Mars can be a habitat for primitive live forms. Pressure of the overlaying rockdetritus, with an average thickness calculated from thermodynamic constrictions of 200 up to 300 meters, maybe melt some waterice, or some water pentrates from deeper zones of the martian crust on the base of the formations and create pockets of liquid water.

And so we are (re) arrived to new frontiers...

P.S.

Until today, rockglaciers are only known from Earth and Mars. Mercury and Venus are much to hot to possess water, or even ice. The gas giants lack a surface, and the minor objects in the solar system seemed to small or to cold to enables creep and deformation of material.But the Voyager in 1979, and the Cassini-Galileo in 1997 mission have provided some images from one of the moons of Jupiter, Callisto.

The high resolution image from the Galileo space probe shows a crater with a lobate deposit, protruding from the craterrim to the centre for 3 to 3.5 kilometers.

The nature of this morphology is still unknown, possible interpretation includes landslides or creep of ice-detritus mixture. The morphology, tonguelike to lobate with a low surface angle and a steep escarpment at the end resemble a rockglacier. But the very low temperature on the surface of Callisto of -180°C does not support creep of water ice. Alternately a different ice component, like methane or other gases, maybe is still capable to deform and so creep along the inner craterrim.

Sonntag, 14. September 2008

Donnerstag, 4. September 2008

Permafrost and his change can affect heavenly infrastructures like streets and buildings in mountain areas above 2.500m a.s.l. To secure existing structures, and provide clues to build and maintain new ones in permafrost affected terrain, exchange of knowledge and experience about the permafrost issue between countries is essential.The now presented “PermaNet – Permafrost Long-term Monitoring Network for the Alpine Space” is planned to provide a platform for permafrost research exchange for at least the next three years. It can be seen as “international version” of a more regional project, ProAlp, that was concluded in July of this year.

The project is funded and promoted trough the “Alpine Space Program”, supported by 7 countries that shares area in the European Alps – Italy, Austria, Slovenia, France, Germany, Swiss and Liechtenstein. One of the main goals of this program is environment and risk preventation, and on point is to research permafrost and related phenomena’s.

PermaNet will be a platform to collect and harmonize data between different institutions and partners in the different countries, to produce a coherent map of permafrost distribution in the European alps and improve models that simulate it’s distribution.Many research and regional projects were carried out in the member countries, so interchange can/should be the next step.

Abo

Just reading

SPÖTL et al.(2006):The last and the Penultimate Interglacial as Recorded by Speleothems From a Climatically Sensitive High-Elevation Cave Site in the Alps. In SIROCKO, F. et al. (ed): The climate of past interglacial. Developments in Quaternary Science 7.